Compilation copyright (c) 1994, 1995, 1996 by Jonathan P. Leech. This
document may be redistributed in its complete and unmodified form. Other
use requires written permission of the author.
PLANETARY PROBES - HISTORICAL MISSIONS
This section was lightly adapted from an original posting by Larry Klaes
(lklaes@aol.com), mostly minor formatting changes. Matthew Wiener
(weemba@libra.wistar.upenn.edu) contributed the section on Voyager, and
the section on Sakigake was obtained from ISAS material posted by
Yoshiro Yamada (yamada@yscvax.ysc.go.jp).
US PLANETARY MISSIONS
MARINER (VENUS, MARS, & MERCURY FLYBYS AND ORBITERS)
MARINER 1, the first U.S. attempt to send a spacecraft to Venus, failed
minutes after launch in 1962. The guidance instructions from the ground
stopped reaching the rocket due to a problem with its antenna, so the
onboard computer took control. However, there turned out to be a bug in
the guidance software, and the rocket promptly went off course, so the
Range Safety Officer destroyed it. Although the bug is sometimes claimed
to have been an incorrect FORTRAN DO statement, it was actually a
transcription error in which the bar (indicating smoothing) was omitted
from the expression "R-dot-bar sub n" (nth smoothed value of derivative
of radius). This error led the software to treat normal minor variations
of velocity as if they were serious, leading to incorrect compensation.
MARINER 2 became the first successful probe to flyby Venus in December
of 1962, and it returned information which confirmed that Venus is a
very hot (800 degrees Fahrenheit, now revised to 900 degrees F.) world
with a cloud-covered atmosphere composed primarily of carbon dioxide
(sulfuric acid was later confirmed in 1978).
MARINER 3, launched on November 5, 1964, was lost when its protective
shroud failed to eject as the craft was placed into interplanetary
space. Unable to collect the Sun's energy for power from its solar
panels, the probe soon died when its batteries ran out and is now in
solar orbit. It was intended for a Mars flyby with MARINER 4.
MARINER 4, the sister probe to MARINER 3, did reach Mars in 1965 and
took the first close-up images of the Martian surface (22 in all) as it
flew by the planet. The probe found a cratered world with an atmosphere
much thinner than previously thought. Many scientists concluded from
this preliminary scan that Mars was a "dead" world in both the
geological and biological sense.
MARINER 5 was sent to Venus in 1967. It reconfirmed the data on that
planet collected five years earlier by MARINER 2, plus the information
that Venus' atmospheric pressure at its surface is at least 90 times
that of Earth's, or the equivalent of being 3,300 feet under the surface
of an ocean.
MARINER 6 and 7 were sent to Mars in 1969 and expanded upon the work
done by MARINER 4 four years earlier. However, they failed to take away
the concept of Mars as a "dead" planet, first made from the basic
measurements of MARINER 4.
MARINER 8 ended up in the Atlantic Ocean in 1971 when the rocket
launcher autopilot failed.
MARINER 9, the sister probe to MARINER 8, became the first craft to
orbit Mars in 1971. It returned information on the Red Planet that no
other probe had done before, revealing huge volcanoes on the Martian
surface, as well as giant canyon systems, and evidence that water once
flowed across the planet. The probe also took the first detailed closeup
images of Mars' two small moons, Phobos and Deimos.
MARINER 10 used Venus as a gravity assist to Mercury in 1974. The probe
did return the first close-up images of the Venusian atmosphere in
ultraviolet, revealing previously unseen details in the cloud cover,
plus the fact that the entire cloud system circles the planet in four
Earth days. MARINER 10 eventually made three flybys of Mercury from 1974
to 1975 before running out of attitude control gas. The probe revealed
Mercury as a heavily cratered world with a mass much greater than
thought. This would seem to indicate that Mercury has an iron core which
makes up 75 percent of the entire planet.
PIONEER (MOON, SUN, VENUS, JUPITER, and SATURN FLYBYS AND ORBITERS)
PIONEER 1 through 3 failed to meet their main objective - to photograph
the Moon close-up - but they did reach far enough into space to provide
new information on the area between Earth and the Moon, including new
data on the Van Allen radiation belts circling Earth. All three craft
had failures with their rocket launchers. PIONEER 1 was launched on
October 11, 1958, PIONEER 2 on November 8, and PIONEER 3 on December 6.
PIONEER 4 was a Moon probe which missed the Moon and became the first
U.S. spacecraft to orbit the Sun in 1959. PIONEER 5 was originally
designed to flyby Venus, but the mission was scaled down and it instead
studied the interplanetary environment between Venus and Earth out to
36.2 million kilometers in 1960, a record until MARINER 2. PIONEER 6
through 9 were placed into solar orbit from 1965 to 1968: PIONEER 6, 7,
and 8 are still transmitting information at this time. PIONEER E (would
have been number 10) suffered a launch failure in 1969.
PIONEER 10 became the first spacecraft to flyby Jupiter in 1973. PIONEER
11 followed it in 1974, and then went on to become the first probe to
study Saturn in 1979. Both vehicles should continue to function through
1995 and are heading off into interstellar space, the first craft ever
to do so.
PIONEER Venus 1 (1978) (also known as PIONEER Venus Orbiter, or PIONEER
12) burned up in the Venusian atmosphere on October 8, 1992. PVO made
the first radar studies of the planet's surface via probe. PIONEER Venus
2 (also known as PIONEER 13) sent four small probes into the atmosphere
in December of 1978. The main spacecraft bus burned up high in the
atmosphere, while the four probes descended by parachute towards the
surface. Though none were expected to survive to the surface, the Day
probe did make it and transmitted for 67.5 minutes on the ground before
its batteries failed.
RANGER (LUNAR LANDER AND IMPACT MISSIONS)
RANGER 1 and 2 were test probes for the RANGER lunar impact series. They
were meant for high Earth orbit testing in 1961, but rocket problems
left them in useless low orbits which quickly decayed.
RANGER 3, launched on January 26, 1962, was intended to land an
instrument capsule on the surface of the Moon, but problems during the
launch caused the probe to miss the Moon and head into solar orbit.
RANGER 3 did try to take some images of the Moon as it flew by, but the
camera was unfortunately aimed at deep space during the attempt.
RANGER 4, launched April 23, 1962, had the same purpose as RANGER 3, but
suffered technical problems enroute and crashed on the lunar farside,
the first U.S. probe to reach the Moon, albeit without returning data.
RANGER 5, launched October 18, 1962 and similar to RANGER 3 and 4, lost
all solar panel and battery power enroute and eventually missed the Moon
and drifted off into solar orbit.
RANGER 6 through 9 had more modified lunar missions: They were to send
back live images of the lunar surface as they headed towards an impact
with the Moon. RANGER 6 failed this objective in 1964 when its cameras
did not operate. RANGER 7 through 9 performed well, becoming the first
U.S. lunar probes to return thousands of lunar images through 1965.
LUNAR ORBITER (LUNAR SURFACE PHOTOGRAPHY)
LUNAR ORBITER 1 through 5 were designed to orbit the Moon and image
various sites being studied as landing areas for the manned APOLLO
missions of 1969-1972. The probes also contributed greatly to our
understanding of lunar surface features, particularly the lunar farside.
All five probes of the series, launched from 1966 to 1967, were
essentially successful in their missions. They were the first U.S.
probes to orbit the Moon. All LOs were eventually crashed into the lunar
surface to avoid interference with the manned APOLLO missions.
SURVEYOR (LUNAR SOFT LANDERS)
The SURVEYOR series were designed primarily to see if an APOLLO lunar
module could land on the surface of the Moon without sinking into the
soil (before this time, it was feared by some that the Moon was covered
in great layers of dust, which would not support a heavy landing
vehicle). SURVEYOR was successful in proving that the lunar surface was
strong enough to hold up a spacecraft from 1966 to 1968.
Only SURVEYOR 2 and 4 were unsuccessful missions. The rest became the
first U.S. probes to soft land on the Moon, taking thousands of images
and scooping the soil for analysis. APOLLO 12 landed 600 feet from
SURVEYOR 3 in 1969 and returned parts of the craft to Earth. SURVEYOR 7,
the last of the series, was a purely scientific mission which explored
the Tycho crater region in 1968.
VIKING (MARS ORBITERS AND LANDERS)
VIKING 1 was launched from Cape Canaveral, Florida on August 20, 1975 on
a TITAN 3E-CENTAUR D1 rocket. The probe went into Martian orbit on June
19, 1976, and the lander set down on the western slopes of Chryse
Planitia on July 20, 1976. It soon began its programmed search for
Martian micro-organisms (there is still debate as to whether the probes
found life there or not), and sent back incredible color panoramas of
its surroundings. One thing scientists learned was that Mars' sky was
pinkish in color, not dark blue as they originally thought (the sky is
pink due to sunlight reflecting off the reddish dust particles in the
thin atmosphere). The lander set down among a field of red sand and
boulders stretching out as far as its cameras could image.
The VIKING 1 orbiter kept functioning until August 7, 1980, when it ran
out of attitude-control propellant. The lander was switched into a
weather-reporting mode, where it had been hoped it would keep
functioning through 1994; but after November 13, 1982, an errant command
had been sent to the lander accidentally telling it to shut down until
further orders. Communication was never regained again, despite the
engineers' efforts through May of 1983.
An interesting side note: VIKING 1's lander has been designated the
Thomas A. Mutch Memorial Station in honor of the late leader of the
lander imaging team. The National Air and Space Museum in Washington,
DC is entrusted with the safekeeping of the Mutch Station Plaque until
it can be attached to the lander by a manned expedition.
VIKING 2 was launched on September 9, 1975, and arrived in Martian orbit
on August 7, 1976. The lander touched down on September 3, 1976 in
Utopia Planitia. It accomplished essentially the same tasks as its
sister lander, with the exception that its seisometer worked, recording
one marsquake. The orbiter had a series of attitude-control gas leaks in
1978, which prompted it being shut down that July. The lander was shut
down on April 12, 1980.
The orbits of both VIKING orbiters should decay around 2025.
VOYAGER (OUTER PLANET FLYBYS)
VOYAGER 1 was launched September 5, 1977, and flew past Jupiter on March
5, 1979 and by Saturn on November 13, 1980. VOYAGER 2 was launched
August 20, 1977 (before VOYAGER 1), and flew by Jupiter on August 7,
1979, by Saturn on August 26, 1981, by Uranus on January 24, 1986, and
by Neptune on August 8, 1989. VOYAGER 2 took advantage of a rare
once-every-189-years alignment to slingshot its way from outer planet to
outer planet. VOYAGER 1 could, in principle, have headed towards Pluto,
but JPL opted for the sure thing of a Titan close up.
Between the two probes, our knowledge of the 4 giant planets, their
satellites, and their rings has become immense. VOYAGER 1&2 discovered
that Jupiter has complicated atmospheric dynamics, lightning and
aurorae. Three new satellites were discovered. Two of the major
surprises were that Jupiter has rings and that Io has active sulfurous
volcanoes, with major effects on the Jovian magnetosphere.
When the two probes reached Saturn, they discovered over 1000 ringlets
and 7 satellites, including the predicted shepherd satellites that keep
the rings stable. The weather was tame compared with Jupiter: massive
jet streams with minimal variance (a 33-year great white spot/band cycle
is known). Titan's atmosphere was smoggy. Mimas' appearance was
startling: one massive impact crater gave it the Death Star appearance.
The big surprise here was the stranger aspects of the rings. Braids,
kinks, and spokes were both unexpected and difficult to explain.
VOYAGER 2, thanks to heroic engineering and programming efforts,
continued the mission to Uranus and Neptune. Uranus itself was highly
monochromatic in appearance. One oddity was that its magnetic axis was
found to be highly skewed from the already completely skewed rotational
axis, giving Uranus a peculiar magnetosphere. Icy channels were found on
Ariel, and Miranda was a bizarre patchwork of different terrains. 10
satellites and one more ring were discovered.
In contrast to Uranus, Neptune was found to have rather active weather,
including numerous cloud features. The ring arcs turned out to be bright
patches on one ring. Two other rings, and 6 other satellites, were
discovered. Neptune's magnetic axis was also skewed. Triton had a
canteloupe appearance and geysers. (What's liquid at 38K?)
The two VOYAGERs are expected to last for about two more decades. Their
on-target journeying gives negative evidence about possible planets
beyond Pluto. Their next major scientific discovery should be the
location of the heliopause. Low-frequency radio emissions believed to
originate at the heliopause have been detected by both VOYAGERs.
SOVIET PLANETARY MISSIONS
Since there have been so many Soviet probes to the Moon, Venus, and
Mars, I will highlight only the primary missions:
SOVIET LUNAR PROBES
LUNA 1 - Lunar impact attempt in 1959, missed Moon and became first
craft in solar orbit.
LUNA 2 - First craft to impact on lunar surface in 1959.
LUNA 3 - Took first images of lunar farside in 1959.
ZOND 3 - Took first images of lunar farside in 1965 since LUNA 3. Was
also a test for future Mars missions.
LUNA 9 - First probe to soft land on the Moon in 1966, returned images
from surface.
LUNA 10 - First probe to orbit the Moon in 1966.
LUNA 13 - Second successful Soviet lunar soft landing mission in 1966.
ZOND 5 - First successful circumlunar craft. ZOND 6 through 8
accomplished similar missions through 1970. The probes were
unmanned tests of a manned orbiting SOYUZ-type lunar vehicle.
LUNA 16 - First probe to land on Moon and return samples of lunar soil
to Earth in 1970. LUNA 20 accomplished similar mission in
1972.
LUNA 17 - Delivered the first unmanned lunar rover to the Moon's
surface, LUNOKHOD 1, in 1970. A similar feat was accomplished
with LUNA 21/LUNOKHOD 2 in 1973.
LUNA 24 - Last Soviet lunar mission to date. Returned soil samples in
1976.
SOVIET VENUS PROBES
VENERA 1 - First acknowledged attempt at Venus mission. Transmissions
lost enroute in 1961.
VENERA 2 - Attempt to image Venus during flyby mission in tandem with
VENERA 3. Probe ceased transmitting just before encounter in
February of 1966. No images were returned.
VENERA 3 - Attempt to place a lander capsule on Venusian surface.
Transmissions ceased just before encounter and entire probe
became the first craft to impact on another planet in 1966.
VENERA 4 - First probe to successfully return data while descending
through Venusian atmosphere. Crushed by air pressure before
reaching surface in 1967. VENERA 5 and 6 mission profiles
similar in 1969.
VENERA 7 - First probe to return data from the surface of another planet
in 1970. VENERA 8 accomplished a more detailed mission in
1972.
VENERA 9 - Sent first image of Venusian surface in 1975. Was also the
first probe to orbit Venus. VENERA 10 accomplished similar
mission.
VENERA 13 - Returned first color images of Venusian surface in 1982.
VENERA 14 accomplished similar mission.
VENERA 15 - Accomplished radar mapping with VENERA 16 of sections of
planet's surface in 1983 more detailed than PVO.
VEGA 1 - Accomplished with VEGA 2 first balloon probes of Venusian
atmosphere in 1985, including two landers. Flyby buses went on
to become first spacecraft to study Comet Halley close-up in
March of 1986.
SOVIET MARS PROBES
MARS 1 - First acknowledged Mars probe in 1962. Transmissions ceased
enroute the following year.
ZOND 2 - First possible attempt to place a lander capsule on Martian
surface. Probe signals ceased enroute in 1965.
MARS 2 - First Soviet Mars probe to land - albeit crash - on Martian
surface. Orbiter section first Soviet probe to circle the Red
Planet in 1971.
MARS 3 - First successful soft landing on Martian surface, but lander
signals ceased after 90 seconds in 1971.
MARS 4 - Attempt at orbiting Mars in 1974, braking rockets failed to
fire, probe went on into solar orbit.
MARS 5 - First fully successful Soviet Mars mission, orbiting Mars in
1974. Returned images of Martian surface comparable to U.S.
probe MARINER 9.
MARS 6 - Landing attempt in 1974. Lander crashed into the surface.
MARS 7 - Lander missed Mars completely in 1974, went into a solar orbit
with its flyby bus.
PHOBOS 1 - First attempt to land probes on surface of Mars' largest
moon, Phobos. Probe failed enroute in 1988 due to
human/computer error.
PHOBOS 2 - Attempt to land probes on Martian moon Phobos. The probe did
enter Mars orbit in early 1989, but signals ceased one week
before scheduled Phobos landing.
While there has been talk of Soviet Jupiter, Saturn, and even
interstellar probes within the next thirty years, no major steps have
yet been taken with these projects. More intensive studies of the Moon,
Mars, Venus, and various comets have been planned for the 1990s, and a
Mercury mission to orbit and land probes on the tiny world has been
planned for 2003. How the many changes in the former Soviet Union (now
the Commonwealth of Independent States) will affect the future of their
space program remains to be seen.
EUROPEAN PLANETARY MISSIONS
GIOTTO was launched by an Ariane-1 by ESA on July 2 1985, and approached
within 540 km +/- 40 km of the nucleus of comet Halley on March 13,
1986. The spacecraft carried 10 instruments including a multicolor
camera, and returned data until shortly before closest approach, when
the downlink was temporarily lost. Giotto was severely damaged by
high-speed dust encounters during the flyby and was placed into
hibernation shortly afterwards.
In April, 1990, Giotto was reactivated. 3 of the instruments proved
fully operational, 4 partially damaged but usable, and the remainder,
including the camera, were unusable. On July 2, 1990, Giotto made a
close encounter with Earth and was retargeted to a successful flyby of
comet Grigg-Skjellerup on July 10, 1992.
A much more complete description of the Giotto Extended Mission is in
ftp://ftp.cs.unc.edu/pub/users/leech/FAQ/GiottoHistory.gz
JAPANESE PLANETARY MISSIONS
SAKIGAKE (MS-T5) was launched from the Kagoshima Space Center by ISAS on
January 8, 1985, and approached Halley's Comet within about 7 million km
on March 11, 1986. The spacecraft is carrying three instruments to
measure interplanetary magnetic field/plasma waves/solar wind, all of
which work normally now, so ISAS made an Earth swingby by Sakigake on
January 8, 1992 into an orbit similar to the Earth's. The closest
approach was at 23h08m47s (JST=UTC+9h) on January 8, 1992. The
geocentric distance was 88,997 km. This is the first planet-swingby for
a Japanese spacecraft.
During the approach, Sakigake observed the geotail. Some geotail
passages will be scheduled in some years hence. The second Earth-swingby
will be on June 14, 1993 (at 40 Re (Earth's radius)), and the third
October 28, 1994 (at 86 Re).
HITEN, a small lunar probe, was launched into Earth orbit on January 24,
1990. The spacecraft was then known as MUSES-A, but was renamed to Hiten
once in orbit. The 430 lb probe looped out from Earth and made its first
lunary flyby on March 19, where it dropped off its 26 lb midget
satellite, HAGOROMO. Japan at this point became the third nation to
orbit a satellite around the Moon, joining the Unites States and USSR.
The smaller spacecraft, Hagoromo, remained in orbit around the Moon. An
apparently broken transistor radio caused the Japanese space scientists
to lose track of it. Hagoromo's rocket motor fired on schedule on March
19, but the spacecraft's tracking transmitter failed immediately. The
rocket firing of Hagoromo was optically confirmed using the Schmidt
camera (105-cm, F3.1) at the Kiso Observatory in Japan.
Hiten made multiple lunar flybys at approximately monthly intervals and
performed aerobraking experiments using the Earth's atmosphere. Hiten
made a close approach to the moon at 22:33 JST (UTC+9h) on February 15,
1992 at the height of 423 km from the moon's surface (35.3N, 9.7E) and
fired its propulsion system for about ten minutes to put the craft into
lunar orbit. The following is the orbital calculation results after the
approach:
Apoapsis Altitude: about 49,400 km
Periapsis Altitude: about 9,600 km
Inclination : 34.7 deg (to ecliptic plane)
Period : 4.7 days
PLANETARY MISSION REFERENCES
I also recommend reading the following works, categorized in three
groups: General overviews, specific books on particular space missions,
and periodical sources on space probes. This list is by no means
complete; it is primarily designed to give you places to start your
research through generally available works on the subject. If anyone can
add pertinent works to the list, it would be greatly appreciated.
Though naturally I recommend all the books listed below, I think it
would be best if you started out with the general overview books, in
order to give you a clear idea of the history of space exploration in
this area. I also recommend that you pick up some good, up-to-date
general works on astronomy and the Sol system, to give you some extra
background. Most of these books and periodicals can be found in any good
public and university library. Some of the more recently published works
can also be purchased in and/or ordered through any good mass- market
bookstore.
General Overviews (in alphabetical order by author):
J. Kelly Beatty et al, THE NEW SOLAR SYSTEM, 1990.
Merton E. Davies and Bruce C. Murray, THE VIEW FROM SPACE:
PHOTOGRAPHIC EXPLORATION OF THE PLANETS, 1971
Kenneth Gatland, THE ILLUSTRATED ENCYCLOPEDIA OF SPACE
TECHNOLOGY, 1990
Kenneth Gatland, ROBOT EXPLORERS, 1972
R. Greeley, PLANETARY LANDSCAPES, 1987
Douglas Hart, THE ENCYCLOPEDIA OF SOVIET SPACECRAFT, 1987
Nicholas L. Johnson, HANDBOOK OF SOVIET LUNAR AND PLANETARY
EXPLORATION, 1979
Clayton R. Koppes, JPL AND THE AMERICAN SPACE PROGRAM: A
HISTORY OF THE JET PROPULSION LABORATORY, 1982
Richard S. Lewis, THE ILLUSTRATED ENCYCLOPEDIA OF THE
UNIVERSE, 1983
Mark Littman, PLANETS BEYOND: DISCOVERING THE OUTER SOLAR
SYSTEM, 1988
Eugene F. Mallove and Gregory L. Matloff, THE STARFLIGHT
HANDBOOK: A PIONEER'S GUIDE TO INTERSTELLAR TRAVEL, 1989
Frank Miles and Nicholas Booth, RACE TO MARS: THE MARS
FLIGHT ATLAS, 1988
Bruce Murray, JOURNEY INTO SPACE, 1989
Oran W. Nicks, FAR TRAVELERS, 1985 (NASA SP-480)
James E. Oberg, UNCOVERING SOVIET DISASTERS: EXPLORING THE
LIMITS OF GLASNOST, 1988
Carl Sagan, COMET, 1986
Carl Sagan, THE COSMIC CONNECTION, 1973
Carl Sagan, PLANETS, 1969 (LIFE Science Library)
Arthur Smith, PLANETARY EXPLORATION: THIRTY YEARS OF UNMANNED
SPACE PROBES, 1988
Andrew Wilson, (JANE'S) SOLAR SYSTEM LOG, 1987
Specific Mission References:
Charles A. Cross and Patrick Moore, THE ATLAS OF MERCURY, 1977
(The MARINER 10 mission to Venus and Mercury, 1973-1975)
Joel Davis, FLYBY: THE INTERPLANETARY ODYSSEY OF VOYAGER 2, 1987
Irl Newlan, FIRST TO VENUS: THE STORY OF MARINER 2, 1963
Margaret Poynter and Arthur L. Lane, VOYAGER: THE STORY OF A
SPACE MISSION, 1984
Carl Sagan, MURMURS OF EARTH, 1978 (Deals with the Earth
information records placed on VOYAGER 1 and 2 in case the
probes are found by intelligences in interstellar space,
as well as the probes and planetary mission objectives
themselves.)
Other works and periodicals:
NASA has published very detailed and technical books on every space
probe mission it has launched. Good university libraries will carry
these books, and they are easily found simply by knowing which mission
you wish to read about. I recommend these works after you first study
some of the books listed above.
Some periodicals I recommend for reading on space probes are NATIONAL
GEOGRAPHIC, which has written articles on the PIONEER probes to Earth's
Moon Luna and the Jovian planets Jupiter and Saturn, the RANGER,
SURVEYOR, LUNAR ORBITER, and APOLLO missions to Luna, the MARINER
missions to Mercury, Venus, and Mars, the VIKING probes to Mars, and the
VOYAGER missions to Jupiter, Saturn, Uranus, and Neptune.
More details on American, Soviet, European, and Japanese probe missions
can be found in SKY AND TELESCOPE, ASTRONOMY, SCIENCE, NATURE, and
SCIENTIFIC AMERICAN magazines. TIME, NEWSWEEK, and various major
newspapers can supply not only general information on certain missions,
but also show you what else was going on with Earth at the time events
were unfolding, if that is of interest to you. Space missions are
affected by numerous political, economic, and climatic factors, as you
probably know.
Depending on just how far your interest in space probes will go, you
might also wish to join The Planetary Society, one of the largest space
groups in the world dedicated to planetary exploration. Their
periodical, THE PLANETARY REPORT, details the latest space probe
missions. Write to The Planetary Society, 65 North Catalina Avenue,
Pasadena, California 91106 USA.
Good luck with your studies in this area of space exploration. I
personally find planetary missions to be one of the more exciting areas
in this field, and the benefits human society has and will receive from
it are incredible, with many yet to be realized.
Larry Klaes klaes@verga.enet.dec.com
NEXT: FAQ #9/13 - Upcoming planetary probes - missions and schedules

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